A number of the current video coding algorithms is based on motion compensated predictive coding schemes. In such schemes, temporal redundancy is reduced using motion compensation, while spatial redundancy is reduced by transform coding the residue of motion compensation. One component of motion compensated predictive coding schemes is motion compensated temporal filtering (MCTF), which is performed to reduce temporal redundancy.
MCTF typically includes filtering frames temporally in the direction of motion. MCTF may be combined with a spatial transform (e.g., wavelet or discrete cosine transform (DCT)) and entropy coding to create the encoded bitstream.
During the temporal filtering, some pixels may either be not referenced or referenced multiple times due to the nature of the motion in the scene and the covering/uncovering of objects. Not referenced pixels are known as unconnected pixels, and pixels referenced multiple times are known as multiply connected pixels. Processing of unconnected pixels by traditional MCTF algorithms typically requires special handling, which leads to reduced coding efficiency. In the case of multiply connected pixels, traditional MCTF algorithms typically achieve the overall temporal transformation as a succession of local temporal transformations, which destroys the orthonormality of the transformation, resulting in quantization noise propagation effects at the decoder.